It is known in the art that microporous fluoropolymer membranes are useful in a variety of applications. Articles made from microporous fluoropolymer membranes possess properties such as toughness, impact strength, abrasion resistance, low coefficient of friction, gamma resistance, and resistance to attack by solvents and corrosive chemicals. Because of the favorable attributes associated with microporous fluoropolymer membranes, microporous fluoropolymer membranes have been utilized in a variety of applications, such as water filtration, dialysis, battery separators, vents, desalinization, and gas separation.
Of the numerous microporous fluoropolymer membranes in existence, polyvinylidene fluoride (PVDF and PVDF copolymer) membranes possess excellent chemical resistance, heat resistance, and radiation resistance. Copolymers of PVDF are also used in piezoelectric and electrostrictive applications. PVDF membranes are conventionally formed by a solvent induced phase separation or a thermally induced phase separation method. However, such conventional processes possess undesirable features or attributes, such as, for example, requiring high solvent levels and processing above the melt temperature of the PVDF polymer. In addition, conventional processes result in a mechanically weak and/or costly article.
Thus, there exists a need in the art for a process for making a PVDF copolymer article that is processed without solvent and below the melting temperature, has high strength, and is highly porous.